Interpretive Summary: Certain nematodes (small round worms) and fungi are able to kill insects and can be used as natural environmentally friendly insect pest control measures. The beneficial nematodes and fungi are called entomopathogenic, which means they kill insects. Fortunately these fungi and nematodes do not harm human, pets, or other non-target organisms. Research is warranted to develop methods that improve the use of entomopathogenic nematodes and fungi for natural pest control. Interactions with other organisms in the soil could help or hinder the use of beneficial nematodes and fungi. We hypothesized that earthworms would enhance the biological control capacity of entomopathgoenic nematodes and earthworms. We reasoned that earthworms would carry the nematodes and fungi through the soil (without hurting them and vice versa) and thereby help the smaller organisms disperse and find insect to attack. This relationship, where one organism is carried by another is called phoresy. Our hypothesis was supported. Our results indicated that an entomopathogenic neamtode species, called Steinernema carpocapsae, was able to disperse better in soil and provide higher levels of insect control, when earthworms were present than when they were absent. The insect we used in the test was the pecan weevil, a major pest of pecans that is known to be susceptible to the nematodes. Similarly, we found that a fungus species, called Beauveria bassiana, was carried by the earthworms. The fungus was deposited in earthworm casts and remianed viable and able to infect insects. Therefore, it may be conceivable to combine the application of earthworms with beneficial organisms such as nematodes and fungi to achieve enhanced levels of natural insect control.

Technical Abstract:
Prior research indicated that earthworms may serve as phoretic hosts to entomopathogenic nematodes. Therefore, we hypothesized that biocontrol efficacy of nematodes could be enhanced in the presence of earthworms based on increased nematode dispersal through the soil. We also hypothesized that earthworms may serve as phoretic hosts to other entomopathogens, such as fungi. We tested the first hypothesis by comparing the ability of two strains of Steinernema carpocapsae to suppress the pecan weevil, Curculio caryae in the presence or absence of the earthworm, Lumbricus terrestris. We tested the second hypothesis by determining the effects of L. terrestris on dispersal of the entomopathogenic fungus Beauveria bassiana in soil columns. Our results indicated that earthworm presence improved the ability of S. carpocapsae (Sal strain) to control C. caryae below the soil surface. Additionally, S. carpocapsae (All strain) only caused significant C. caryae suppression relative to the controls in the presence of earthworms. Beauveria bassiana dispersal was enhanced by earthworm presence. The fungus was carried through soil by the earthworm; conidia recovered from the earthworm casts remained viable and was pathogenic to Galleria mellonella. Earthworms and other phoretic hosts may assist in dispersal of entomopathogenic nematode and fungal populations in various ecosystems and thereby assist in regulation of insect pests. Additionally, it may be conceivable to combine the application of earthworms with entomopathogens to achieve enhanced levels of inundative or inoculative biocontrol.